Mobile IP is a protocol designed to allow mobile units, e.g. third generation cellular phones, laptop computers, etc. to roam between various sub-networks at various locations, while still maintaining Internet and/or WAN connectivity. In order to further discuss this type of operation, let us first explain some basic functional entities associated with mobile IP networks.
A number of solution has been proposed in the past to enable smooth hand over in cellular networks. Some of these solutions are described herein.
U.S. Pat. No. 6,741,577 discloses a method for inter-frequency handover in wireless CDMA systems which tries to decrease the likelihood of dropped calls by reducing bit error-rate while increasing the spreading factor.
U.S. RE 37,787 relates to a method in mobile radio systems in which the responsibility for transmitting message information to a mobile station is handed over from a first base station transmitter to a second base station transmitter, while the same radio channel is used before and after the handover, and the transmission is started from the second base station transmitter before terminated from the first base station transmitter, so that during a certain transmission time the same message information is transmitted to the mobile station from both the first and second base station transmitters.
U.S. Pat. No. 5,384,826 describes a cellular switching system in which the switching associated with a call originated within one cell but now serviced within another cell is distributed among base stations which are interconnected with each other through a local area network or a packet switch. The routing procedure associated with the point of origin for a given call is stored in the memory of a switch of public switched telephone network. As an active subscriber crosses a cell boundary, the switch routes all packets of information for the given call to the originating base station for the duration of the call. Each base station then forwards each packet to the subscriber's current base station via the local area network. In this manner, the architecture is unaffected by the increased crossing between cell boundaries since the switching associated with those calls not within the range of the initial base station is handled in a distributed manner by each base station via the local area network.
WO 05/006781 discloses a method and apparatus for facilitating base station selection/handover by a user terminal in a distributed wireless communication system. According to this disclosure, hysteresis is adaptively determined as a function of the variance of received signal strength fluctuations. In turn, an adaptive hysteresis factor is obtained and used for a subsequent handover decision, for example, based on a cost function that takes into account the hysteresis.
U.S. Pat. No. 6,728,540 describes handing over an ongoing communication with a mobile in a current cell of a wireless cellular system another cell, using information regarding a set of potential handover candidates. This information is transmitted from a base station in the current cell or from another fixed part transmitter in the system. The set of handover candidates for a given mobile in the current cell is determined based on stored adjacency information regarding the cells which are adjacent to the current cell. This adjacency information is stored after an initial system configuration, based on the actual physical layout of the cells, and may be altered during system operation to reflect the success or failure of particular attempted handovers. The set of potential handover candidates includes corresponding channel identifying information such as frequency and time slot and the potential handover candidate information is transmitted upon receipt of a handover assistance request from the mobile.
The disclosure of the references mentioned herein throughout the present specification are hereby incorporated by reference.
Still none of the solutions suggested in the past provides an adequate solution to the problem of hand over in a mobile packetized wireless network, and in particularly there are no solutions that enable preservation of data flow integrity during such hand over.